1. Field of the Invention
The present invention relates to a contact charger for use in image forming apparatus such as electrophotographic copying machines and printers.
2. Related Art of the Invention
In electrophotographic copying machines, printers and like image forming apparatus, an electrostatic latent image bearing member such as a photosensitive drum is charged by a charger, and the charged area is exposed to light to form thereon an electrostatic latent image, which is then developed to a visible image and thereafter transferred and fixed to a copy sheet.
Various types of chargers are known which are divided generally into those of the noncontact type utilizing corona discharge, and those of the contact type wherein a brush, roller or drivingly revolvable endless belt is held in contact with the surface of the electrostatic latent image bearing member, or wherein a blade made of rigid body is pressed against one point on the surface of the image bearing member and voltage is applied to the blade.
The chargers of the noncontact type utilizing corona discharge have the advantage of effecting stabilized charging, but possess the problem of producing a large amount of ozone which deteriorates the image bearing member and exerts an adverse influence on the human body. Attention is therefore directed to the chargers of the contact type which are much smaller than the corona chargers in the amount of ozone produced.
Among the chargers of the contact type, however, those employing the brush have the problem that the production of the brush requires labor, while those wherein the roller or endless belt is used need means for driving the roller or belt, and are therefore correspondingly more complex in construction. Moreover, the roller remains in contact with the image bearing member even while the image forming apparatus is out of operation, is accordingly subjected to residual strain due to creep and consequently fails to effect proper charging. Furthermore, the charger having the endless belt has the problem of being large-sized in its entirety and necessitating a complex belt drive system. The charger having the blade encounters difficulty in setting the blade in position because the blade, which is a rigid body, is not smoothly in contact with the the surface of the image bearing member, and has the likelihood of defacing the image bearing member since the blade is held in contact with the image bearing member surface under high pressure. Because of the high pressure, the electrostatic latent image bearing member further needs a great torque for rotation.